1. Field of the Invention
A subject matter of the invention is an aliphatic or semi-aliphatic polyester composition plasticized by a specific diol ester. Another subject matter of the invention is a process for manufacturing said composition and uses of this composition. Another subject matter of the invention is the use of this diol ester as plasticizer for an aliphatic or semi-aliphatic polyester.
2. Description of the Related Art
The use of plastics has become widespread in numerous applications. The amounts of plastic which are produced and used worldwide have thus significantly increased in recent years, resulting in an increase in the volume of waste and in environmental problems.
In order to facilitate the removal of this plastic waste, biodegradable polymers are forming the subject of very particular interest.
Mention may be made, as an example of biodegradable polymer, of “biodegradable polyethylene”, which is in reality composed of non-biodegradable polyethylene and of an additive which makes it possible to render it biodegradable.
These advantageous polymers also include aliphatic or semi-aliphatic polymers which, by virtue of their specific structure, exhibit an intrinsic biodegradable nature even in the absence of an additive.
The term “semi-aliphatic polyester” is understood to mean any polyester comprising at least 70 mol % of aliphatic units, that is to say of units devoid of an aromatic ring.
The term “aliphatic polyester” is understood to mean any polyester exclusively composed of aliphatic units.
The term “unit” in a polyester is understood to mean any unit which can be obtained by polycondensation of monomers forming polyesters, namely monomers chosen from dicarboxylic acids, diols and hydroxy acids.
By way of example, poly(lactic acid) (PLA), poly(glycolic acid) (PGA) and polycaprolactone (PCL) are aliphatic polyesters resulting from hydroxyalkanoic acid. Mention may be made, as polyester obtained by polycondensation of a diol and of a dicarboxylic acid, of poly(butylene succinate) (PBS), which is an aliphatic polyester, or also of poly(butylene adipate-co-terephthalate) (PBAT), which is a semi-aliphatic polyester resulting from the polycondensation of butanediol, of an aliphatic dicarboxylic acid (adipic acid) and of an aromatic dicarboxylic acid (terephthalic acid).
However, these polyesters can exhibit a number of disadvantages. In particular, their mechanical properties may be insufficient for certain uses. For example, PLA, in particular highly crystalline PLA, exhibits a very low elongation at break at ambient temperature (of the order of a few percent only) and is thus very brittle. In order to be able to use them in more numerous applications, it is necessary to improve the properties of these polyesters. For this, these polyesters can be blended with “plasticizers”.
The term “plasticizer” is understood to mean any product which, when it is mixed in a sufficient amount with a polymer, has the role of reducing the glass transition temperature of said polymer.
By reducing the glass transition temperature of the polymer, the flexibility of the latter is increased and the mechanical properties of this plasticized polymer are modified. Thus, on adding, to a polymer composition, a plasticizer for the latter, a decrease in the Young's modulus, a decrease in the tensile strength and/or an increase in the strain at break are generally observed. These modified properties of the polymer make it possible for it to be used in more numerous applications, for example in flexible films.
However, a plasticizer used for a certain type of polymer is not necessarily suitable for another type of polymer.
Mention may be made, by way of example, of the document EP0523789 A1, which describes plasticization tests on PLA with numerous known plasticizers. Glycerol trioleate, glycerol decanoate, propylene glycol, glycerol trihexanoate, glycerol, triacetin, lactates and citrates, which are known plasticizers for polyvinyl chloride (PVC), do not or insufficiently plasticize PLA, are not compatible with PLA or have an insufficient plasticizing effect.
Reference may also be made to chapter 11 of the Handbook of Plasticizers (Wypych G., ChemTec Publishing, 2004, pages 273-379), which specifies the plasticizers which can be used according to each type of polymer; these appropriate plasticizers are different according to the polymer targeted.
The effect of the plasticization of PLA on the mechanical properties has also been studied by Jocobsen et al. in the paper Plasticizing polylactide-the effect of different plasticizers on the mechanical properties (Polymer Engineering and Science, 1999, Vol. 39, No. 7, pages 1303-1310). A polyethylene glycol, a partially esterified fatty acid or a glucose monoester are introduced into the PLA in amounts by weight of less than or equal to 10%. Polyethylene glycol is the most efficient plasticizer. The plasticization of the PLA remains insufficient, as is shown by the very low elongation at break values.
Various citrates are also evaluated as plasticizer in PLA by Labrecque et al. in the paper Citrate Esters as Plasticizers for Poly(lactic acid) (Journal of Applied Polymer Science, 1997, Vol. 66, No. 8, pages 1507-1513). No cyclic diol ester is described as plasticizer in this document. Furthermore, these esters are not very stable thermally and exhibit a high volatility, which brings a significant loss of the plasticizer during the preparation of the plasticized PLA composition.
Ketals are also described in the application US 2008/0242721 as plasticizers for polymers, including PLA or poly(3-hydroxyalkanoic acid).
Different plasticizers for poly(hydroxyalkanoic acid) are also disclosed in the application WO 02/085983, including paraffin, epoxy compounds, polyols, fatty acid or dicarboxylic acid esters, oils, glycerol esters or phosphates. However, no cyclic diol ester is described as plasticizer in this document.
The document EP 2 143 743 A1 describes, for its part, a process for the preparation of resin, in which a 1,4:3,6-dianhydrohexitol ester derivative is used in this process as solvent, co-solvent and/or coalescence agent and not as plasticizer. A mixture comprising a polyester oligomer, which comprises 60 mol % of saturated aliphatic units, of other monomers and oligomers, and also an isosorbide diether: dimethyl isosorbide, is described in table 1. This intermediate mixture is subsequently used for the manufacture of polyurethane.
Thus, none of the current solutions is entirely satisfactory for the plasticization of aliphatic or semi-aliphatic polyesters.
Furthermore, another problem of the products manufactured from these polyesters is the level of sound nuisance which can accompany their use.
This is because, during the handling of the product by the final consumer, the noise created can be very loud, this particularly being the case when said product comprises sheets or films of these polyesters, which are generally the case with packagings.
By way of example, as a result of the dissatisfaction of consumers, Frito Lay® in 2010 had to withdraw bags of chips which they had placed on the American market and which were packaged in material produced from PLA because the noise was too great when the consumer of the chips opened or handled the bag.
Similar problems could also be observed in plants for the manufacture of articles made of PLA, in particular when these objects are obtained by extrusion.
There thus still exists at the current time a need to find novel plasticized compositions based on these polyesters, these compositions exhibiting:                an increased flexibility in comparison with the polyester alone,        a greater strain at break than that of the polyester alone,        a faint odor,        and/or good compatibility of the plasticizer with the polyester, making possible good blending of the plasticizer and polyester during the manufacture and a low, indeed even non-existent, exudation of the plasticizer from a polymer during use.        
It is also advantageous to be able to find a composition based on one of these polyesters which makes possible the manufacture of objects for which the handling is not excessively loud, indeed even also to limit sound nuisance during the manufacture of said object.
Furthermore, it is advantageous for the plasticizer used not to volatilize or not to volatilize to any great extent during the manufacture of this composition.